High power superluminescent diodes (SLD) have applications in fiber optic gyroscopes (FOG), optical amplifiers, external cavity lasers, tunable laser, mode-locked lasers, and in general, as light sources for applications requiring low coherence, such as low coherence interferometers (for fault detection and certain medical instrumentation and imaging). In such uses, it is often necessary to couple the output of the diode into an optical fiber, particularly a single mode optical fiber. Thus, it is desirable to be able to control the size and divergence angle of the emitted beam of radiation so that it can be easily coupled into the optical fiber.